Slow charging in general is not a problem.
If you have 50 cells in parallel without fuses on each cell, even slow charging could become a problem. Suppose at some point one cell should decide to go rogue and short circuit. Now you have 49 cells discharging all they can through that one cell, causing a likely hazardous situation.

For testing, you could use ATC fuses/holders, or even glass barrel fuses/holders. They'd be easy to replace and fairly cheap and no soldering required. Use the 2.5A fuses and you should be just fine. 5A would fine as well. But since your testing these, I'd go with the 2.5A to start with.

That's fine I'm playing with my monitoring solution, think I've got a few ideas to string together. Which will include fuses. Looking for a thin material, that I can use to mock up my wiring and support the cell holders. Then it's the long wait for for parts from China ...............

This is my ghetto slow charging setup to boost cells drained down to say 2.0V ~ 2.8V. Anything below now gets tossed.
I make sure the cells all have the same voltage, then use tiny magnets and metal paper clips to connect the cells in parallel. Then use a lab power supply set to 3.3V / max 30mA (or more, depending on the number of cells). The alligator clips conveniently snap on to the previously mentioned magnets.
I do up to 4 cells this way.